LED control, in general, cannot be accomplished solely through the precise control of LED manufacturing variables, since the operating environment of the LED (temperature, current stability, infiltration of other light sources, etc.) may affect the color and intensity of the LED device. Known feedback control systems are used to control color and intensity of LEDs. One such known system involves the use of multichannel light sensors tuned to each color in the system. For example, a typical RGB system includes a string of red LEDs, a string of green LEDs and a string of blue LEDs. A multichannel RGB light sensor is placed in proximity to the light source in a location that is optimized to receive light flux from all three emitters. The sensor outputs signals indicative of the average total flux and the color point of the RGB system. A feedback controller compares this information to a set of preset or user-defined values. The multichannel sensor adds complexity and cost to the system design and architecture, and, in most cases, suffers from a lack of 1:1 correspondence between the light sensor and LED channels, making the color point calculations complex and limiting their accuracy.
Another known feedback control system utilizes a broadband sensor to sense the light from the LED channels. To control each individual channel, all other channels must be turned off so that the sensor can “focus” on a single color at a time. Thus, this system does not lend itself to continuous, simultaneous and independent control of all the channels in the system.